NORFOLK, Va. — Republican presidential candidate Mitt Romney this morning tapped Rep. Paul Ryan of Wisconsin as his vice presidential running mate, turning to the architect of a conservative and intensely controversial long-term budget plan to remake Medicare and cut trillions in federal spending.

Romney made his announcement to supporters via a phone app. “Mitt’s Choice for VP is Paul Ryan,” it said and implored backers to spread the word.

The ticket-mates arranged their first joint appearance later in the morning at a naval museum, the initial stop of a bus tour through four battleground states in as many days.

In a written statement, Romney’s campaign said that Ryan, 42, has worked in Congress to “eliminate the federal deficit, reform the tax code and preserve entitlements for future generations.”

Ryan’s selection — as well as Romney’s own nomination — will be ratified by delegates to the Republican National Convention that begins on Aug. 27 in Tampa, Fla.

President Barack Obama and Vice President Joseph Biden will be nominated for a second term at the Democratic convention the following week.